Crooked grass (4)
I believe the answer is:
bent
I believe this clue is a double definition.
'crooked' is the first definition.
(both can mean corrupt)
'grass' is the second definition.
(I know that bent is a type of grass)
(Other definitions for bent that I've seen before include "Dishonest; angled" , "Out of shape, curved" , "Corrupt; grass stalk" , "Slang for dishonest or crooked" , "leaning" .)